Polymers are at present used as additives in asphalts and bitumens used for roads or in industry, either for improving their workability by modifying the hot rheological properties, or for improving their physicochemical properties (cold brittleness, toughness, flexibility, stability, thermal susceptibility, mechanical strength with respect to shocks, vibrations, abrasions, etc.)
In general, the polymers used are thermoplastics (olefin copolymers or polymers), rubbers and in particular thermoplastic elastomers (multiblock copolymers of diolefins and styrene), or, to a lesser extent, thermosetting resins (polyurethanes, epoxy resin, phenol formaldehyde). According to the prior art, these polymers can be used alone or in mixture. For example, it has been proposed to recycle as additives in bitumens, production waste (waxes of polyethylene, atactic polypropylene, polyvinyl alcohol, powdered vulcanized rubber waste, etc.) or plastic waste from household refuse and more specifically plastic packing materials. In the latter case, the mixtures of polymers essentially contain polyolefins, polyvinyl chloride, polystyrene and polyethylene terephthalate.
The polymers are added in small quantities (generally 2 to 10% by weight) to bitumens, in the form of "simple" mixtures involving no chemical reaction or interaction between the constituents, or in the form of "complex" mixtures involving a chemical reaction or interaction between the polymer and certain constituents of the bitumen (asphaltenes, malthenes, resins, etc.), optionally in the presence of a third constituent (catalyst, reagent). Usually the polymers are dispersed in the solid or melted state in a previously heated excess of bitumen and, after stirring, the mixtures are either molten used state, or cooled to the solid state and optionally granulated or ground. Certain processes for the production of a mixture in the molten state of bitumens for roads to which have been added olefin polymers recommend the addition of at least 5 to 30% by weight of mineral particles, which speed up the dissolving of the polymer in the bitumen (cf., e.g., U.S. Pat. No. 3,336,252 published on Aug. 15, 1967). U.S. Pat. No. 4,028,293, published on June 7, 1977, claims the production of a bitumen-containing material more particularly used for roads and construction purposes and which is obtained by the high temperature reaction (at at least 180.degree. C.) of a mineral compound, such as sand or gravel, with a polymer or a mixture of polymers obtained from domestic or household refuse. The resultant mixture is then added hot to the bitumen and cooled. A major disadvantage of this method is the final cost of the operation, which requires a preheating to high temperature of a significant quantity of mineral material prior to the addition of the polymer or polymers.
The present invention relates to a simplified, economic process for the recycling of polymer waste in bitumens for roads or industry. This process is particularly suitable for the recycyling of "sterile car waste", i.e., plastic waste resulting from the breaking up of cars and which may possibly contain other polymer waste materials in small proportions, e.g., resulting from the breaking up of electric domestic appliances.
The generic name "sterile car waste" or "car crushing waste" in fact designates all mineral and organic materials resulting from the crushing or cutting into pieces of in particular car bodies and to a lesser extent electric domestic appliances and industrial waste and obtained after the separation of the main metallic materials, e.g., by magnetic sorting processes, by gravitation or hydrocyclones, by flotation or performed manually. The recovered metallic materials are recycled as starting or raw materials for the metallurgical industry. However, the recycling of "sterile" or non-metallic waste at present constitutes a major problem due to the heterogeneity of the material which is a mixture having a variable composition and constituted by non-metallic mineral particles and various polymers such as expanded materials or foams, vulcanized rubber materials, synthetic fibers, thermoplastics and thermoset resins.
Bearing in mind the increasing quantities of polymer materials used in the construction of vehicles and electric household appliances, it has become necessary to find new means for getting rid of such sterile materials and which are satisfactory both from economic and ecological standpoints. It has already been proposed to dispose of most "sterile car waste" by incineration, as in the case of domestic refuse. Although the construction of specific incinerators for "sterile car waste" is technically possible, it does not at present constitute the most satisfactory solution from the energy and financial standpoints, bearing in mind the ecological constraints linked with ensuring the particulate removal from the combustion smoke and fumes and the prevention of discharges of toxic or corrosive gases. As in the case of plastic waste from packing and domestic refuse, consideration has also been given to the recycling of "sterile car waste" as second generation starting materials, used alone or mixed with new, first generation materials. However, in view of their more heterogeneous composition, the uses of "sterile car waste" as recycled materials have remained very limited up to now and have not made it possible to envisage a sufficiently large scale use to get rid of the increasing quantities thereof. Therefore most "sterile car waste" is at present stored in protected dumps, which involves ever higher storage costs and which, despite all the precautions taken, constitutes a relatively unsatisfactory solution from the environmental standpoint.